【作者】 罗建；

【导师】 肖鹏；

【作者基本信息】 中南大学 ， 材料物理与化学， 2023， 硕士

【摘要】 硅基复合材料被认为是下一代锂离子电池负极材料,但硅基负极材料存在充放电过程中巨大的体积变化和低本征电导率两大固有问题,会造成电极粉化、失去电接触和差的倍率性能,从而影响硅基负极材料的实际应用。本文针对上述硅基材料的固有问题,以及多孔硅基材料制备复杂、纳米硅材料高成本等商业问题,从金属复合、涂层设计和结构优化等方面,改进制备了微米级多孔硅基复合材料,主要包含以下几个方面:（1）以微米级的铝硅合金粉末（Al-Si）作为原材料,硫酸为刻蚀溶液,控制反应时长,得到不同Al含量的多孔Si球,发现化学刻蚀4 h后得到的含Al多孔Si球的结构完整、孔隙清晰,少量Al元素在多孔Si骨架上分布均匀。内部的孔隙可为硅基材料提供膨胀空间,金属Al可大幅提升复合材料的电子传导率,从而提升材料的电化学性能。最终含Al多孔Si球在0.5 A g^-1的电流密度下,经过150次循环,可以保持977 m Ah g^-1的比容量。（2）为了进一步提高含Al多孔Si球的电子传导率,以及缓解硅基材料的膨胀问题,通过湿化学的方法,以盐酸多巴胺为碳源,制备出含Al多孔Si@C复合材料,微球粒径在1μm左右,碳涂层均匀包覆在含Al多孔Si球表面,厚度约为10 nm;最终,含Al多孔Si@C复合材料在0.5 A g^-1的电流密度下,初始库伦效率为81.9%,经过250次循环,可以展示550 m Ah g^-1的比容量,在电流密度为1 A g^-1的条件下,经过125次循环后表现出802 m Ah g^-1的可逆比容量,当电流密度升为5 A g^-1时,仍有859 m Ah g^-1的良好比容量。（3）利用甲醛和间苯二酚的聚合反应,在微米级的Al-Si球表面形成酚醛树脂涂层;为充分发挥硅基材料的容量,后用硫酸将复合材料中的Al元素全部刻蚀;先包覆酚醛树脂层,后进行刻蚀的方法可以避免多孔结构的破坏;最终以钛酸四丁酯为钛源,结合热处理,制备出具有双涂层的PSi@C@TiO₂复合材料。微球大小在1μm左右,球形结构完整,未出现多孔结构坍塌的现象,内部无定形碳层和外部锐钛矿型TiO₂层的厚度分别大约为10 nm和20 nm;内部完整的孔隙可以容纳硅核的膨胀,碳层可加速电子转移,高强度的TiO₂层可维持球形结构的稳定。最终PSi@C@TiO₂电极在0.5 A g^-1的电流密度下,经过250次循环,依然可以保持1004 m Ah g^-1的比容量,在电流密度为1 A g^-1的条件下,经过150次循环后表现出851 m Ah g^-1的可逆比容量,且在5 A g^-1的倍率下可以保持745 m Ah g^-1的良好比容量。在循环过程中,PSi@C@TiO₂微球表面形成稳定的SEI膜,多孔球形结构依旧保持完整,双涂层的厚度并未发生较大变化,且循环100圈之后的电极膨胀率仅为35.3%。图64幅,表8个,参考文献145篇更多还原

【Abstract】 Silicon-based materials are considered as the next generation of anode material for lithium-ion batteries.However,when silicon-based materials are used as LIBs anode,there are two inherent problems of huge volume change during charging and discharging and low intrinsic conductivity.These problems can cause electrode pulverization,loss of electrical contact and poor rate performance,which affect the practical application of silicon-based anode materials.In this paper,we improve the preparation of microscale porous silicon-based composites in terms of metal compounding,coating design and structural optimization to improve the electrochemical performance by addressing the inherent problems of silicon-based materials mentioned above,as well as the commercial problems of complicated preparation of porous silicon-based materials and high cost of nano silicon materials,which mainly consist of the following aspects:（1）Microscale Al-Si alloy powder（Al-Si）was used as the raw material,and the etching solution are sulfuric acid.Then,the reaction time was controlled to obtain porous Si spheres with different Al contents.It is found that the Al-containing porous Si spheres obtained after 4 h of chemical etching has complete structure and clear pores,small amounts of Al elements are uniformly distributed on the porous silicon skeleton.The internal pores can provide expansion space for the silicon-based material and the Al elements can significantly improve the electron conductivity of the composite,thereby improving the electrochemical properties.Finally,the Al-containing porous Si microspheres can maintain a specific capacity of 977 m Ah g^-1 after 150 cycles at a current density of 0.5 A g^-1.（2）To further improve the electron conductivity of the Al-containing porous Si microspheres and to alleviate the swelling problem of silicon-based materials,the Al-containing porous Si@C composite was prepared by the polymerization reaction of dopamine hydrochloride.The particle size of the Al-containing porous Si@C spheres is around 1μm,and the carbon layer is uniformly coated on the surface of the Al-containing porous Si spheres with a thickness of about 10 nm;the Al-containing porous Si@C electrode exhibits an initial coulombic efficiency of 81.9%,which also demonstrates a specific capacity of 550 m Ah g^-1after 250 cycles at a current density of 0.5 A g^-1 and a reversible specific capacity of 802 m Ah g^-1 after 125 cycles at a current density of 1 A g^-1,moreover,the Al-containing porous Si@C composite can maintain a good specific capacity of 859 m Ah g^-1 at a high rate of 5 A g^-1.（3）The phenolic resin layer was firstly coated on the surface of the microscale Al-Si spheres by using the polymerization reaction;all Al elements in the composite were etched with H₂SO₄to exploit the high capacity of the silicon-based material;the method of coating the phenolic resin layer first and etching later could avoid the collapse of the porous structure;finally,PSi@C@TiO₂ composites with double shell were prepared by sol-gel and heat treatment.The size of PSi@C@TiO₂microspheres with intact porous structure is around 1μm,the thickness of the inner amorphous carbon layer and the outer anatase TiO₂ layer are about 10 nm and 20 nm,respectively.As a result,the PSi@C@TiO₂electrode can still maintain 1004 m Ah g^-1 after 250 cycles at a current density of 0.5 A g^-1and a reversible specific capacity of 851 m Ah g^-1 after150 cycles at a current density of 1 A g^-1,moreover,it can maintain a good specific capacity of 745 m Ah g^-1 at a high rate of 5 A g^-1.During the cycling process,a stable SEI film is formed on the surface of PSi@C@TiO₂microspheres,the porous spherical structure remains intact,and the thickness of the double shell do not change significantly,resulting in the electrode expansion rate of 35.3%after 100 cycles.更多还原